New poop symptom seen in mysteriously ill 6 week old. Dry, chalky, light colored poop?

[Sparrow]

I have been posting about my cochin chick who, despite vitamin b12 and vitamin e treatment, appears to be going downhill. I have noticed today that his poop is now very dry, kind of chalky feeling, and a very light greyish-tan color where it should be brown. It is perfectly well formed, you have to break it with your fingers to feel the weird texture(sounds gross but whatever). He is progressively looking weaker and thinner the past few days. His original symptoms are below, as I posted previously.

Classic symptoms of either problem. Started with finding him laying on his back randomly. Flip him over, and he was all wobbly in the legs. He would stand but look woozy and off balance. It has progressed to him not flipping as much now because he spends most of his time laying down in a strange position. Very rarely he has the one leg in front, other out back. Usually it is more on his his belly or rolled to his side. Legs are not stiff, feet limp but not curled. If he tries, he can still move the legs, but they just seem to lack he strength to stand him up all the way nowdays. Breast and thighs are thin. He has eaten well until today, he looks much worse and weaker today, unfortunately. No skin lesions, no eye oddities. He has been down for two weeks, no other chicks appear affected.

Does this strange new symptom ring a bell for anyone?